The invention is based on a fuel injection pump for internal combustion engines.
In a fuel injection pump of this type, known from Japanese Patent Application 261 667/87, the fuel injection quantity is split during the high-pressure pumping into a pre-injection quantity and a main injection quantity. This provision enables reducing the prestorage of uncombusted fuel during the ignition delay, and accordingly, overly high pressure peaks in the combustion chamber upon sudden combustion of the prestored fuel can be avoided, which in turn lessens the thermal and mechanical strain on the engine and provides noise abatement. To that end, in the known pump, besides the diversion bores in the annular slide that control the high-pressure pumping and the control recesses, and the transverse and longitudinal bores in the pump piston that connect the control recesses to the pump work chamber formed in the cylinder liner by the pump piston, a first exemplary embodiment also has a pocket in the inner wall of the annular slide, and the pocket cooperates with a transverse bore in the pump piston that discharges into the longitudinal bore.
In a second embodiment of this known fuel injection pump, during the crossover of the additional transverse bore in the pump piston that discharges into the longitudinal bore the pocket in the annular slide is additionally made to communicate with a pocket likewise made in the pump cylinder, via an additional connecting conduit disposed in the pump piston. In the high-pressure pumping of the pump piston, which begins when the control recesses on the pump piston plunge into the annular slide and when the communication between the pump work chamber and the suction chamber surrounding the annular slide is closed off, an interruption in the pressure rise in the pump work chamber occurs, because upon the crossover of additional transverse bore communicating with the pump work chamber via the longitudinal bore, fuel compressed in the pump piston flows out of the pump chamber into the pocket disposed in the annular slide, causing the pressure in the pump work chamber to drop. This pressure drop persists until a pressure equilibrium has been established between the fuel flowing into the pocket and the fuel located in the pump work chamber. From that moment on, the fuel pressure in the pump work chamber increases again, and the pumping of the main injection quantity takes place, which ends when the control recesses on the pump piston are opened as a result of the crossover of the diversion bores in the annular side. High-pressure fuel pumping is accordingly interrupted by the opening of the additional filling volume and the attendant pressure drop, and in the variant embodiment described as a second embodiment, this interruption is greater because of the larger volume to be filled. During the intake stroke of the pump piston that follows the pumping stoke, the additional pockets, which are at high fuel pressure, are pressure-relieved again via communication with the pump suction chamber.
Since storage takes place during this known type of interruption of the high-pressure pumping, the pressure in the pump work chamber does not drop far enough that the injection valves connected to it via an injection line will close and the injection will be fully interrupted. The known fuel injection pump also has the disadvantage that the connecting conduit in the pump piston, between the pocket in the annular slide and the pocket in the pump cylinder, can be produced only with a major effort and at a great expense.